The previous grant period involved an integrated study of the toxicity of various anti-tumor agents on the hemopoietic and immunopoietic systems. We propose to focus our study on more detailed mechanisms of toxicity of the following groups of anti-tumor agents: cell-cycle-stage-specific (CCSS) and non-specific (CCSN) and bacterial and viral products (B & V). The overview obtained in the past years of our granting period is that, in vivo, precursor cells (CFU and CFC) of the hemopoietic system are the likely targets of anti-tumor agents. We shall employ the following techniques to determine drug effects on precursor cells: suiciding, cell separation, use of anti-seras, and the use of the lymphocytic CFC assay. By studying the effects of these agents in tumor-bearing mice, we hope to identify the mechanisms of toxicity to precursor cells of the hemopoietic system at various stages of tumor growth.